Nitrogen oxides, such as NO and NO2 (collectively referred to as NOx), generated in the high temperature and high pressure conditions of an internal combustion engine, may constitute a large percentage of total exhaust emissions. Accordingly, engine exhaust systems may utilize selective catalytic reduction (SCR) to reduce the NOx species to diatomic nitrogen and water. To meet new lower NOx level requirements, many internal combustion engine vehicles are using a separate reductant (i.e., reducing agent) stored in the vehicle. In the United States, the Environmental Protection Agency requires that a customer be informed of the level of reductant in the reductant tank, and that the manufacturer compel the vehicle operator to refill the reductant tank before empty, to maintain proper emissions control.
Previous solutions include limiting engine speed as the reductant becomes scarce, and preventing a restart of the vehicle if the reductant tank is empty. The inventors of the present application have recognized a problem in such previous solutions, in that completely disabling the engine may cause inconvenience to the vehicle operator, in that the vehicle may be made inoperable when the vehicle operator is in a rural area without easy access to reductant. Further, preventing restart of the vehicle may reduce the comfort of the vehicle's occupants.
In one example, some of the above issues may be addressed by a method for controlling a vehicle having an engine with an exhaust, the exhaust having a reductant injection system including a reductant storage vessel, the engine further having a fuel system including a fuel storage vessel, the method comprising, under degraded reductant conditions, restricting vehicle motion in response to a fuel refill of the fuel storage vessel. The degraded reductant conditions may include the level of stored reductant being below a threshold, and/or the stored reductant having improper make-up (e.g., a reductant storage vessel is filled with water, not reductant).
By restricting vehicle motion in response to a fuel refill, there is a higher likelihood that the vehicle operator is at a location where reductant (e.g., urea) is available, such as at a service station. Further, it may also be likely that having just filled the fuel storage vessel, the vehicle operator may be motivated to simply obtain the reductant while at the service station. Additionally, although such restricting of vehicle motion may limit transmission drive gear engagement, for example, engine idling may still be enabled, thus enabling HVAC operation for the vehicle operator and passengers. Further, in some embodiments, a vehicle operator may issue an override command to override vehicle restriction of vehicle motion under selected conditions. By allowing such an override, it may again be possible to accommodate unusual circumstances and give the vehicle operator more opportunity to refill the reductant storage vessel. Further still, in some embodiments, messages issued to the vehicle operator may be tied to future levels of restriction. For example, such messages may indicate a future action that will be implemented as a consequence for not refilling the reductant storage vessel when degraded reductant conditions are present.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.